This invention relates to Quality of Service improvements in wireless LAN systems. Some embodiments relate specifically to quality of service enhancements in the IEEE 802.11 WLAN standard.
The IEEE's standard for wireless LANs, designated IEEE 802.11, provides two different ways to configure a network: ad-hoc and infrastructure. In an ad-hoc network, computers form a network on the fly, wherein each computer or 802.11 device joining the network is able to send and receive signals. There is no defined structure in an ad-hoc network; there are no fixed points; and every node in the network is able to communicate with every other node in the network. Although it may seem that order would be difficult to maintain in this type of network, sufficient algorithms, such as the spokesman election algorithm (SEA), are provided and are designed to elect one machine as the base, or master, station of the network, with the others machines being slaves. Another algorithm in ad-hoc network architectures uses a broadcast and flooding method to all other nodes to establish the identity of all nodes in the network.
The infrastructure architecture of an exemplary network comprising 802.11-like wireless devices and connectivity is shown in FIG. 1. In a typical network, wireless network stations 32 & 34 that share wireless connectivity in a first Basic Service Area (BSA) 40 may be organized into a first Basic Service Set (BSS1) 42 that can be controlled by a single coordination function. A network may comprise a plurality of BSSs that are linked together. A second BSS 44 (BSS2), comprising wireless stations 46 & 48 that may exist within a network, but outside the BSA 40 of a first BSS 42. These stations may be able to communicate with each other within a second BSA 50, but do not have the range or other capability to access stations 32 & 34 outside their BSA 50. Coordination within a BSS 42 & 44 may be controlled by coordination functions comprising a Distributed Coordination Function (DCF) and a Point Coordination Function (PCF). When using a PCF, a single station 32, 34, 46 or 48 within a BSS 42 or 44 performs coordination function logic. This PCF station may also serve as an Access Point (AP) 34, 46 that controls access to network elements outside of the BSS 42, 44.
Wired networks 52 may also be connected to wireless network BSSs 42, 44 through portals 54 that implement distribution system service (DSS) functions to access a distribution system (DS) 56 that connects to BSS APs 34, 46 thereby forming a single functional network. A plurality of BSSs 42, 44 may also be linked through an Extended Service Set (ESS) 58 that links BSSs into a single logical network.
APs may act as fixed network access points for communications with mobile stations. These APs may be connected to land lines to widen the LAN's capability by bridging wireless nodes to other wired nodes. If service areas overlap, handoffs may occur between wireless LANs. This structure is very similar to that used in cellular networks.
The IEEE 802.11 standard places specifications on the parameters of both the physical (PHY) and medium access control (MAC) layers of the network. The PHY layer, which actually handles the transmission of data between nodes, may use either direct sequence spread spectrum, frequency-hopping spread spectrum, or infrared (IR) pulse position modulation. IEEE 802.11 makes provisions for data rates of up to 11 Mbps, and requires operation in the 2.4-2.4835 GHz frequency band, in the case of spread-spectrum transmission, which is an unlicensed band for industrial, scientific, and medical (ISM) applications; and in the 300-428,000 GHz frequency band for IR transmission. Infrared is generally considered to be more secure to eavesdropping, because IR transmissions require absolute line-of-sight links, i.e., no transmission is possible outside any simply connected space or around corners, as opposed to radio frequency transmissions, which can penetrate walls and be intercepted by third parties unknowingly. However, infrared transmissions can be adversely affected by sunlight, and the spread-spectrum protocol of 802.11 does provide some rudimentary security for typical data transfers. The 802.11b physical layer (PHY) provides data rates up to 11 Mbps using a direct sequence spread spectrum (DSSS) approach; while 802.11a provides data rates up to 54 Mbps using an orthogonal frequency division multiplex (OFDM) approach.
The MAC layer includes a set of protocols which is responsible for maintaining order in the use of a shared medium. The 802.11 standard specifies a carrier sense multiple access with collision avoidance (CSMA/CA) protocol. In this protocol, when a node receives a packet to be transmitted, it first listens to ensure no other node is transmitting. If the channel is clear, it then transmits the packet. Otherwise, it chooses a random backoff factor, which determines the amount of time the node must wait until it is allowed to transmit its packet. During periods in which the channel is clear, the transmitting node decrements its backoff counter. When the channel is busy it does not decrement its backoff counter. When the backoff counter reaches zero, the node transmits the packet. Because the probability that two nodes will choose the same backoff factor is small, collisions between packets are minimized.
Collision detection, as is employed in Ethernet®, cannot be used for the radio frequency transmissions of IEEE 802.11, because when a node is transmitting, it cannot hear any other node in the system which may be transmitting, because its own signal will block any other signals arriving at the node. Whenever a packet is to be transmitted, the transmitting node may first send out a short ready-to-send (RTS) packet containing information on the length of the packet. If the receiving node hears the RTS, it responds with a short clear-to-send (CTS) packet. After this exchange, the transmitting node sends its packet. When the packet is received successfully, as determined by a cyclic redundancy check (CRC), the receiving node transmits an acknowledgment (ACK) packet. This back-and-forth exchange is necessary to avoid the hidden node problem, i.e., node A can communicate with node B, and node B can communicate with node C. However, node A cannot communicate with node C. Thus, for instance, although node A may sense the channel to be clear, node C may in fact be transmitting to node B. The protocol described above alerts node A that node B is busy, and requires node A to wait before transmitting its packet.
Although 802.11 provides a reliable means of wireless data transfer, some improvements to it have been proposed. The use of wireless LANs is expected to increase dramatically in the future as businesses discover the enhanced productivity and the increased mobility that wireless communications can provide.
IEEE Standard 802.11 (1999) for wireless local area networks (WLAN) does not support Quality of Service (QoS) traffic delivery in its MAC layer. A method to provide Quality of Service traffic delivery for IEEE Standard 802.11 WLAN systems is desirable to enhance communications reliability for 802.11 devices.
There is an 802.11 Task Group e (TGe) joint proposal to support QoS enhancements. Virtual streams having QoS parameter values including priority, data rate, delay bounds and jitter bounds, are supported. The proposal uses an enhanced point coordination (PC) function (EPCF), featuring centralized contention control for sending reservation request frames to request new bandwidth allocations. Several new data and management frames are used. New acknowledgement policies, direct station-to-station transfers, basic service set (BSS) overlap management, and dynamic wireless repeater functions are included. This proposal requires modification of the existing 802.11 standard, and may not support, or be supported by, legacy 802.11 devices.
The subject IEEE standard is set forth in ISO/IEC 8802:1999(E) IEEE Std 802.11, 1999 edition, International Standard [for] Information Technology—Telecommunications and information exchange between systems—Local and metropolitan area networks—Specific Requirements—Part 11: Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) specifications.
QoS issues are discussed in the following references:U.S. Pat. No. 6,049,549 to Ganz et al., granted Apr. 11, 2000, for Adaptive medium control, describes an approach to QoS having a polling manager, which uses just in time polling based on allocated bandwidth, and a resource manager, which provides admission control and allocates network resources.
U.S. Pat. No. 5,970,062 to Bauchot, granted Oct. 19, 1999, for Method and apparatus for providing wireless access to an ATM network, describes an ATM MAC approach to QoS.
U.S. Patent No. 5,787,080 to Hulyalkar et al., granted Jul. 28, 1998, for Method and apparatus for reservation-based wireless ATM local area network, describes a reservation-based mobile wireless MAC-arbitrated QoS method for use with automated teller machines. The techniques are not compatible with packet-data WLANs.
U.S. Pat. No. 5,745,480 to Behtash et al., granted Apr. 28, 1998, for Multi-rate wireless communications system, describes a communication-negotiated QoS for use in a wireless radio system provided by directly modifying the encoding used to allocate the desired bandwidth, however, such a system is not compatible with packet-data WLANs.